The Dread Wolf's connection to Mythal was established in Dragon Age: Inquisition during the quest What Pride Had Wrought, where a shrine to Fen'Harel appeared early on in Mythal's temple. This is expanded upon later during the epilogue and the DLC Dragon Age Inquisition: Trespasser, where it becomes clear Solas and Mythal had a close relationship through their interactions and their relative statues always appearing close to one another. While it's clear they were close during the reign of the Evanuris, another connection may make itself clear in Dragon Age: Dreadwolf.
While their story may have ended when Mythal was murdered, Solas and Mythal's role in shaping Thedas might have continued thousands of years later during the fall of the Tevinter Imperium. BioWare never explicitly mentions it in the franchise, but certain sources and codex entries hint at the pair appearing at a very key point in Thedas' history. Dragon Age: Dreadwolf presents an opportunity for this to be confirmed.
Dragon Age's Dread Wolf Wasn’t The Only Elven Rebel
Thedas has its share of elven heroes even if many of them have been lost to time and ethnic cleansing. One of the heroes purged from the Chantry's Chant of Light and featured in the Dissonant verses is the elven hero Shartan, who led the elven people in a slave rebellion to victory against Tevinter with Andraste. Players meet a shade that mimics the form of Shartan in the classic Dragon Age: Origins in the Gauntlet, the final resting place of Andraste and the Urn of Sacred Ashes.
In The World of Thedas: Volume II, the introduction to the Dissonant Verses states that Shartan might not have been a real person, and instead based on stories of an ancient elven rebel, which sounds a lot like Solas. Whether this was true, or if Solas had influenced the dreams of the elven slaves from the Fade, it's clear Solas had a hand in the fall of Dragon Age's Tevinter Imperium. The elven slaves overthrew their Tevinter masters and joined Andraste's rebellion. The parallels become even more clear when comparing Solas' original tarot card with Shartan's image in the Chantry, especially if you consider Dagna's comparison of the anchor to a "key".
Dragon Age's Andraste and Mythal May be the Same Person
Mythal endured as a wisp after her murder, and it's likely she had other hosts before Flemeth. The codex entry The Children of Andraste discusses how all of Andraste's biological children were girls, much like Flemeth's daughters. All iconography of Andraste also depicts her with a very specific headdress that only appears on Knight-Commander Meredith, Flemeth, and one of the figures in Dragon Age's red lyrium idol.
Mythal appeared to Flemeth after a great injustice was done to her, and the same could have been done to Andraste, who claimed to have heard the voice of the Maker. As Mythal was the Goddess of Justice and ultimately a warrior god, leading an army to overthrow the magical regime that had unleashed the Blight and possibly opened the prison of those who had murdered her is not far outside the realm of the character's goals. As it's heavily implied and outright stated in several sources across the series, Dragon Age's Andraste was probably a mage, making her the perfect candidate as a vessel of Mythal.
The Implications of Solas and Mythal as a Team in Dragon Age: Dreadwolf
If Andraste and Shartan were ultimately Mythal and Solas working together to free the People and overthrow Tevinter even thousands of years after the fall of the elves, it's possible this may be confirmed or referenced during Dragon Age: Dreadwolf. It might even mean they're working together even as it seems like Mythal is plotting against Solas.
As Inquisition shattered so much of the lore of Dragon Age's Thedas, players can probably expect revelations that shake up even more established history. This can be especially true from characters like Solas and Mythal, who are several thousand years old and have had their hand in shaping the world of Thedas as players know it.
Dragon Age: Dreadwolf is in development.